A sliding member for wet clutches which is subjected to nickel-phosphorus plating is disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 4-181022 as high frictional metallic materials suitable for sliding members of power transmission device. Moreover, a metallic belt member for continuously variable transmissions which is subjected to electrolytic nickel plating is disclosed in Japanese Examined Patent Publication (KOKOKU) No. 6-41780.
However, it is not possible for these sliding members which are subjected to nickel-phosphorus plating, electrolytic nickel plating, and the like, to stably produce a desired high friction coefficient. This results from the fact that film peeling is likely to occur because the stress generated in the interface between films and substrates enlarges when the friction coefficient is high so that the adhesion strength is not effected sufficiently between films and substrates by conventional filming processes. Therefore, it is necessary to enhance the adhesion strength between films and substrates in order to maintain a stably high friction coefficient.
In Japanese Unexamined Patent Publication (KOKAI) No. 7-149583 and Japanese Unexamined Patent Publication (KOKAI) No. 8-262445, there are disclosed sliding members covered with amorphous hard carbon films whose major components are carbon and hydrogen. The amorphous hard carbon films have attracted the attention of engineers, because they show a low friction coefficient and excellent wear resistance, though they exhibit high adhesion strength of films on substrates. However, conventional amorphous hard carbon films which do not contain silicon or nitrogen exhibit a low friction coefficient even under wet conditions using lubricating oil, and are not suitable for members, which are desired to exhibit a high frictional property, such as sliding members for power transmissions.
Moreover, in component parts for power transmissions, it is also necessary to inhibit the occurrence of self-excited vibrations (shudder) of entire vehicles, self-excited vibrations which result from the stick-slip of sliding portions. In order to inhibit shudder, regarding the velocity dependent characteristic of friction coefficient (μ−v characteristic), it is desired that the tendency of lowering friction coefficient, that is, the μ−v negative gradient tendency be lower as sliding velocity increases. In general, however, the higher friction coefficient is, the more it is likely that the μ−v negative gradient tendency enlarges. Therefore, sliding members suitable for component parts in power transmission device are required to exhibit not only a high frictional characteristic but also a favorable μ−v characteristic.
Moreover, since those with high aggressiveness to mating materials cause wear to mating members to impair their optimum sliding surface profile, it is a problem that a desirable frictional characteristic cannot be maintained either.
It has not been possible for conventional wet sliding members to fully satisfy all of these characteristics.
Hence, an object of the present invention is to provide a high frictional sliding member which has higher adhesion strength of the coatings on the substrate, which exhibits wear resistance, whose mating-member aggressiveness is low, and which exhibits a high frictional characteristic and a favorable μ−v characteristic.